1. Field of the Invention
This invention relates to anti-friction bearings, and particularly to mechanisms for supplying liquid lubricant to the anti-friction elements. In a preferred embodiment of the invention, the bearing is a sealed bearing assembly having a self-contained supply of lubricant.
2. Description of Prior Developments
It is known to provide lubrication systems for anti-friction bearings. One problem with many lubricated bearings is that during high speed bearing operation the lubricant tends to be centrifugally thrown radially outwardly against the bearing outer wall. The lubricant forms an outer lubricant ring or liquid annulus spaced away from the anti-friction elements. The anti-friction elements become starved of lubricant.
The lubricant starvation problem can at least partly be solved by more completely filling the bearing with lubricant, i.e. by adding enough lubricant so that the anti-friction elements are continually immersed in lubricant, even when the lubricant is centrifugally formed into a lubricant annulus. However, with a greater quantity of lubricant in the bearing, the anti-friction elements and associated separator or spacer are required to plow through the lubricant mass. The bearing thus requires a greater amount of energy to achieve a given shaft rotational speed.
The higher energy requirement is particularly noticeable during high speed operation during which the energy is translated into objectionable heat in the lubricant and in the bearing elements. Adequate dissipation of the excessive heat is sometimes a problem.
The present invention is concerned with a high speed bearing assembly adapted to use a relatively small quantity of liquid lubricant, but without experiencing the above-mentioned lubricant starvation problem associated with centrifuging of the lubricant into an unusable lubricant annulus. The present invention employs an impeller or scoop arranged to extend a slight distance into the lubricant annulus for hurling the scooped liquid radially inwardly toward the anti-friction elements.
The dynamics are such that the hurled liquid is in the form of a mist of fine droplets. The liquid mist efficiently lubricates the rolling elements without creating significant internal heating of the rolling elements. The rolling elements do not have to plow through a continuous liquid lubricant mass, which would necessitate a high energy expenditure and create a turbulent fluid shear heating of the lubricant.
The use of a liquid scoop means in a lubricated bearing is shown in U.S. Pat. No. 3,753,605 to K. G. Lehmann. The Lehmann patent uses anti-friction element spacer blocks 16 that have angled shoulder surfaces 36 adapted to scoop and deflect liquid lubricant radially inwardly against an inner race 12. The deflected liquid then flows radially outwardly through passages 44 in the spacer blocks, thence through a slot-like passage 42 onto the surface of anti-friction ball element 14.
One disadvantage of the Lehmann arrangement is that the scoop shoulders 36 are within the rolling plane of rolling elements 14 and remote from the outer race 10. The liquid annulus has to form a relatively thick layer on the race 10 surface before the scoop shoulders can engage the liquid annulus. Also, the scooped liquid is required to take a relatively long circuitous route through passages 44 and 42 before reaching the ball element surface. The lubricant passages 42 and 44 will exert sufficient frictional resistance on the flowing liquid that the liquid is in a continuous state when it comes into contact with the ball 14 surface. Lubricant is supplied to the ball surface as a solid liquid stream, not as a mist of fine liquid droplets.
The physical construction of the Lehmann lubricant-distributing mechanism is such that a relatively large quantity of lubricant has to be charged into the bearing assembly before the scoop shoulders 36 can engage the liquid annulus and pump liquid lubricant onto the ball element surfaces. The ball elements have to plow through a substantial quantity of liquid during high speed operation and during low speed operation.